1. Field of the Invention
The present invention relates to the use of fluorescence spectroscopic imaging, more particularly to the use of fluorescence spectroscopic imaging to diagnose tissue damage.
2. Description of Related Art
Proper characterization of tissue damage (e.g., burns and cuts) is needed for determining an appropriate level of treatment. For example, superficial, partial thickness burns typically heal with conservative management impairment. However, for a burn wound that penetrates the full-thickness of the dermis, surgical intervention may be needed to remove damaged tissue and to cover the wound. Therefore, the characterization of tissue damage as, for example, a superficial versus a penetrating burn, is important for determining a treatment.
Prior methods of tissue damage characterization have proved to be unreliable and subject to human error. Clinical appraisals of burn damage, including wound depth, are based on observable tissue color and sensitivity. Studies have shown that even an experienced surgeon may be unable to correctly categorize burn depth in as many as one-third of wounds. Histological sections are an alternative to clinical appraisals and can be used to determining burn wound depth. However, sectioning has been criticized because of its invasive nature, the need for multiple biopsies, sampling error, delay in diagnosis due to fixation time and the need for an experienced pathologist.
Advances in surgical techniques have compounded the problem of tissue damage characterization. For example, laser tissue welding implements a laser beam to join tissues without sutures, thus, a surgeon or other medical personnel needs to characterize the treatment as well as the damage. This distinction can be difficult to make using known techniques.
Tissue welding can also be referred to as tissue fusion or vessel anastomosis. Tissue welding uses laser light energy to activate photo-thermal bonds and/or photo-chemical bonds within targeted tissues. Laser tissue welding can be used alone or in combination with sutures and/or staples to improve strength and/or sealing characteristics. Besides lasers, which operate with wavelengths in the ultra violet, visible and infrared electromagnetic spectrums, other forms of energy, such as radio and microwave frequencies, can be used to join tissues by fusing component proteins.
Laser tissue welding has many advantages over conventional suture techniques, such as a reduction in foreign body reaction (e.g., to sutures, staples, etc.), increased rate of healing, lower constriction of tissues and reduced surgical time. Although success has been achieved in experimental and clinical applications, previous work indicates that the bursting strength of laser assisted blood vessel anastomoses is less than that of a conventional suture. Further, in some cases aneurysm formation can be higher than 6 to 29 percent. One reason for these disadvantages is that the intensity of laser irradiation on a weld site is not well proportioned to the tissue damage, therefore, overheating of the tissue can occur. In order to proportion the laser to the damage, precise tissue damage characterization is needed.
Other laser therapies, such as laser angioplasty, laser recanalization, laser photocoagulation and laser interstitial hyperthemia, also depend on heating a target area. When the photons are absorbed by the tissue, the energy is transformed into heat causing the temperature to rise in the region of adsorption (excited region). One or more photon excitations can lead to protein denaturation, coagulation, and/or ablation.
All heating therapies depend on the selective control of thermal energy delivery and the degree of thermal tissue damage. Therefore, a need exists for a system and method for in situ detection and characterization of tissue damage and treatment.
A method for monitoring a biological tissue is provided, including the steps of illuminating the tissue, including a fluorophore, with a wavelength of light, the wavelength selected for exciting the fluorophore, determining a fluorescent emission intensity of the fluorophore, the emission indicating the presence of the fluorophore, and correlating an emission of the fluorophore to an extent and a degree of damage to the tissue.
Damage to the tissue includes a breakdown of the fluorophore, resulting in a reduced intensity of emission. The fluorophore can include one of collagen and elastin. The fluorophore can include tryptophan, nicotinamide adenine dinucleotide, flavin and porphyrin.
Correlating the emission of the fluorophore to the extent and degree of damage further includes correlating the emission over time, controlling the power of a laser welder based on the correlation, and preventing overheating of the tissue by the laser welder. The laser tissue welder implements a beam of light having a bandwidth in the absorption bands of water.
The method further includes the step of selecting a wavelength based on the tissue""s native concentration of one or more fluorophores, wherein a fluorophore of the highest native concentration is selected for correlation to the extent and degree of damage.
The step of determining a fluorescent emission intensity further comprises the step of determining a relative concentration of the fluorophore over time. The method can further monitor the damage based on the correlation. The damage can include, among others, thermal damage including electrocution, chemical burns, blunt trauma, cuts, and scrapes.
According to an embodiment of the present invention, a method for monitoring a biological tissue is provided. The method illuminates the tissue including collagen with an illumination bandwidth of about 10 nm to about 100 nm of light and a wavelength between about 340 nm to about 380 nm. The method determines a fluorescent emission intensity of the collagen at an emission wavelength of about 380 nm, an intensity of emission indicating the presence and relative amounts of the collagen over time. Further, the method correlates an emission of the collagen to an extent and a degree of thermal damage to the tissue over time. The method controls the power of a laser welder based on the processed correlation and prevents overheating of the tissue by the laser welder. Similarly, emissions of elastin can be monitored, but at longer wavelengths. These methods correlate an emission intensity in real time and/or in situ.
The laser tissue welder can implement a beam of light having a wavelength in the absorption bands of water. The laser tissue welder can implement a beam of light having a wavelength in the absorption bands of collagen.
According to an embodiment of the present invention a monitoring device is provided for detecting thermal damage to a biological tissue and controlling a laser tissue welder. The device includes an illumination device providing a light, a filter provided adjacent to the illumination device to reduce the heat of the light, an optical fiber for directing the filtered light toward the tissue, and a narrow band filter for selecting a bandwidth of light from the filtered light, the bandwidth selected for exciting an emission from a fluorophore of the tissue. The device also includes a camera for collecting a fluorescent emission from the fluorophore, the emission in response to the selected bandwidth of light, a processor for detecting a variation in an emission intensity over time and in response to treatment by the laser tissue welder, and a control means for varying the power of the laser tissue welder in response to a control signal from the processor.
The processor further includes a correlation means for determining the extent and the degree of the thermal damage. The processor can detect a relative concentration of the fluorophore int eh tissue over time.
The laser tissue welder implements a light beam having a wavelength between about 1150 nm and about 1500 nm. The laser can be a Cunyite laser, a Forsterite laser, or similar tissue welding laser having a light beam with a wavelength selected for the absorption bands of water and/or a fluorescent protein.